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NAS How To

Background

Updated: December 29, 2008

For Network Storage devices tested before 29 December 2008, please see this procedure.

From the inception of our NAS Performance Charts, Don Capps' Iozone has been our primary NAS test tool. IOzone is a filesystem benchmark tool that generates and measures a variety of file operations. It's been ported to many machines and runs under many operating systems, is free and even comes with source code!

For this update of our NAS test process, we investigated other tools. But we decided to continue to use Iozone in order to maintain consistency in testing as we transition to a new hardware platform.

Iozone also is OS and application neutral, i.e. it does not rely on or use OS-level optimizations, such as those implemented by Microsoft Vista for file copy operations. Finally, Iozone's ability to easily test throughput over a range of file sizes makes it easy to obtain valuable insight into NAS performance.

Table 1: Current NAS Test bed iozone computer

More memory
The 512 MB of RAM in the old testbed ensured that cache effects were eliminated when the 1 GB file size was tested. But most systems today run with at least 1 GB of RAM and, with Vista, more often 2 GB. So RAM was increased to better reflect today's systems.

PCIe gigabit NIC
The PCI-based NIC in the old testbed limited maximum performance test capability to approximately 67 MB/s. The PCIe NIC in the new testbed provides a network connection speed of 113 MB/s.

Table 2: NAS Test Machine

The last three bullets bear some explanation. The RAID 0 array is not needed by Iozone, which does not access the hard drive on the machine that it runs on when running the actual reads and writes to the target filesystem. It is being added, along with the Vista SP1 OS to support new read and write file copy benchmarks.

We are adding the Vista SP1 filecopy benchmark with mixed feelings. One one hand, Vista will soon join the ranks of Windows Me as an OS that we'd all rather forget. Microsoft has stopped actively marketing Vista and the drumbeat has started on its successor, Windows 7.

But the arguments for Vista (and SP1 specifically) are that it really does deliver higher filecopy performance (see How To Build a Really Fast NAS - Part 6: The Vista (SP1) Difference for the full story). And since it comes on most new PCs, the installed base is significant and growing. The addition of a filecopy benchmark should also help to satisfy those who find it difficult to understand the Iozone throughput vs. filesize plots and just want to know how fast their filecopy will be.

Setup

The Iozone machine and NAS-under-test are connected via a gigabit or 10/100 switch, as the benchmark dictates. The gigabit switch automatically handles jumbo frames up to 9K.

The Tests

The Iozone benchmarks will continue to be run using a 64 KB record size, for consistency and because this record size is still widely used. However, to reflect the increased RAM size on both the NAS testbed and some high-end NASes, file sizes up to 4 GB will now be tested.

This creates a binary file format file of results in Excel compatible format, with the record and file sizes described above. CPU utilization of the IOzone test bed is also logged and checked to ensure that it is not a factor in the test results.

Results are imported into the NAS Chart Database, where they are available in both average (Figure 1) and throughput vs. filesize (Figure 2) forms.

Figure 1: Average Throughput Benchmark Chart

Figure 2: Throughput vs. File Size Chart

The benchmarks consist of Write and Read transfers of a single test folder containing a single non-compressed ripped DVD. The 4.35 GB (4,680,843,264 bytes) folder contains 38 files of various sizes ranging from 1 GB to 10 KB.